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LM2453TA bảng dữ liệu(PDF) 6 Page - National Semiconductor (TI) |
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LM2453TA bảng dữ liệu(HTML) 6 Page - National Semiconductor (TI) |
6 / 14 page G1 DRIVER/BOOST Electrical Characteristic Targets and Limits (See Figure 13 for Test Circuit) Unless otherwise noted: V CC = +80V, VBB = +8V, TC = 50˚C, VREF = 1.735V, HEATSINK MUST BE GROUNDED VIA LOW HF IMPEDANCE. Symbol Parameter Conditions Min Typ Max Units I G1-H Typical G1 High Output Voltage V BLANK Input Low, See (Note 7). 49 V DC V G1-L Typical G1 Low Output Voltage V BLANK Input Low, See (Note 7). 6 V DC V G1PP Typical G1 Output Swing 43 V P-P V G1TH G1 Blanking Input Threshold 0.9 V V 120BOOST Typical 120V Boost Supply 123 V I BOOST Typical 120V Boost Charge Current 50 mA Note 7: Input from signal generator: VHIGH > 2VDC,VLOW < 0.5 VDC;tHIGH = 300 µs, tLOW = 10 ms. Rise/fall time <0.1 µs. 120V Boost/G1 Drive Test Circuit Theory of Operation The LM2453 is a high voltage monolithic three channel CRT driver and three-channel DC clamp circuit suitable for high- resolution display applications. The device also contains a G1 blanking signal driver, which also can be used to gener- ate a 120 VDC supply to power the DC clamp circuit. The LM2453 operates using 80V and 8V power supplies. An ex- ternal supply can also be used to power the clamp circuit if the user desires to do so. The part is housed in the industry standard 15-lead TO-220 molded plastic power package. A simplified circuit block diagram of the LM2453 is shown in Figure 1. A reference supply of approximately 1.7 VDC is supplied to pin 9 of the device. This provides a reference level for the minus input of the video and clamp buffer ampli- fiers as well as for the vertical blank comparator. The output of the buffer amplifier drives the video amplifier which pro- vides a gain of -52 to the input signal and only amplifies the portion of the input signal that is above the reference volt- age. When the input signal is at or below V REF the video out- puts are driven to the +80V supply rail. The output of the driver is a low impedance complimentary emitter follower cir- cuit that minimizes the effect of capacitive load variations on transient response. The clamp amplifier provides a gain of 73 and only amplifies the portion of the input signal that is below the reference volt- age. When the input signal is at or above V REF the clamp outputs are driven to the V boost/120V supply rail. The vertical blank comparator drives the boost circuit, which generates a 40 V p-p signal that can directly drive typical G1 capacitive loads. When the first vertical blanking pulse is received, the G1 drive output enters a current limited latched state until the 120V boost capacitor is fully charged. Thereafter, the G1 output pulses in response to the vertical blanking pulse re- ceived on the multiplexed V REF signal line. Figures 4, 11, 13 show the typical test circuits for evaluation of the LM2453. Application Hints INTRODUCTION National Semiconductor (NSC) is committed to provide ap- plication information that assists our customers in obtaining the best performance possible from our products. The follow- ing information is provided in order to support this commit- ment. The reader should be aware that the optimization of performance was done using a specific printed circuit board designed at NSC. Variations in performance can be realized due to physical changes in the printed circuit board and the application. Therefore, the designer should know that com- ponent value changes might be required in order to optimize performance in a given application. The values shown in this document can be used as a starting point for evaluation pur- poses. When working with high bandwidth circuits, good lay- out practices are always critical to achieving maximum per- formance. DS101302-13 FIGURE 13. 120V Boost/G1 Drive Test Circuit www.national.com 6 |
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